How to configure LVM

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How to configure LVM in linux rhel5 / Centos

Logical Volume Management[LVM]

Every system contains Physical Volums[PV] Such as hard disks, partitions or external storages Volume management treats PVs as sequences of chunks

called Physical Extents (PEs) There is an another concept also Logical Extents(LE) Each LE maps one-to-one PE The system pools LEs into a Volume Group (VG) We can extend this VG by adding a group of Logical extents to it from anywhere at anytime Uses of LVM:

1 Extending the partitions online

2 Grouping of hard disks

3 Reducing the partitions/hard dsik size (offline)

4 Increasing the performance

5 Taking Backup (SNAPSHOT)

Example:

Here we are going to discuss a Volume Group(VG) created from 3Physical

Voumes(PV) And in that VG we'll create two Logival Volumes(LV) And mount it

to /linux1 and /linux2 respectively.

Now first of all in our example, we have 3 partitions In real industry it may be 3 different hard disks

Let it be (1) /dev/sda5 (2) /dev/sda6 (3) /dev/sda7 each of size300Mb.

[root@vm4 ~]# fdisk -l

/dev/sda5 429 465 297171 8e Linux LVM

Steps:

First we will convert this partions(hard disks) into Physical Volumes(PV) Then we'll create a Volume Group (VG) from thosePV s Then inside that VG, We'll create

two Logical Volumes (LV)and we'll mount those for use.

Step1: Creating Physical Volume(PV)s.

Partitions or disks can be converted into PV s using the following Command.

#pvcreate PARTITION_NAMES

#pvcreate /dev/sda5 /dev/sda6 /dev/sda7

or as below

#pvcreate /dev/sda{5,6,7}

[root@vm4 ~]# pvcreate /dev/sda5 /dev/sda6 /dev/sda7

Physical volume "/dev/sda5" successfully created

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Monitoring or verifying the PV s:

You can verify the PV s using following commands,

#pvscan

#pvdisplay

#pvs

[root@vm4 ~]# pvs

PV VG Fmt Attr PSize PFree

/dev/sda5 lvm2 290.21M 290.21M

/dev/sda6 lvm2 290.21M 290.21M

/dev/sda7 lvm2 290.21M 290.21M

Step2: Creating Volume Group(VG):

The Physical Volumes are grouped into one to make it a Volume Group(VG) It can be

done using the following command

#vgcreate VG_NAME PV_NAMES

#vgcreate oracle /dev/sda5 /dev/sda6 /dev/sda7

or as below

#vgcreate oracle /dev/sda{5,6,7}

It will have a appoximate size of 900(300+300+300) Some part will for writing headers

LE and making LE-PE mapping

[root@vm4 ~]# vgcreate oracle /dev/sda5 /dev/sda6 /dev/sda7

Volume group "oracle" successfully created

[root@vm4 ~]# vgs

VG #PV #LV #SN Attr VSize VFree

oracle 3 0 0 wz n- 864.00M 864.00M

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Monitoring or verifying the VG s:

You can verify the VG s using following commands,

#vgscan

#vgdisplay

#vgs

Output of #vgs is shown above the picture

Step3: Creating Logical Volumes In Volume Group:

Now we got a volume group "Oracle" of size as the total size of all individual disks/partitions Now we can create Logical Volumes or usable partitions inside it We will create two logical Volumes lvm1 andlvm2 of size 100Mb each.

The lvm1 and lvm2 can be created using the following commands

#lvcreate -L SIZE -n LV_NAME VG_NAME

#lvcreate -L 100M -n lvm1 oracle

[root@vm4 ~]# lvcreate -L 100M -n lvm1 oracle

Logical volume "lvm1" created

[root@vm4 ~]# lvcreate -L 100M -n lvm2 oracle

Logical volume "lvm2" created

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Monitoring or verifying the LV s:

You can verify the LV s using following commands,

#lvscan

#lvdisplay

#lvs

[root@vm4 ~]# lvs

LV VG Attr LSize Origin Snap% Move Log Copy% Convert

lvm1 oracle -wi-a- 100.00M

The Logical Voumes lvm1 and lvm2 should be formatted(making filesystem in those) before mounting it Then only you can use those partitions

Here formatting in ext3:

#mkfs.ext3 /dev/oracle/lvm1

#mkfs.ext3 /dev/oracle/lvm2

Making Mount Points:

#mkdir /linux1

#mkdir /linux2

Mounting (Temporary):

#mount /dev/oracle/lvm1 /linux1

#mount /dev/oracle/lvm2 /linux2

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[root@vm4 ~]# mount

[Output truncated]

/dev/mapper/oracle-lvm1 on /linux1 type ext3 (rw)

/dev/mapper/oracle-lvm2 on /linux2 type ext3 (rw)

Extending a Logical Volume (Online):

Now We have a Volume group "oracle" of size about 900Mb And two Logical vloumes lvm1 and lvm2 mounted on /linux1 and /linux2 respectively Each having 100Mb size Now we'll extend the size of lvm1 by 50Mb

Extending size of a LV can be done online, That is by keeping them mounted It can be achived by executing following command

#lvextend -L +SIZE THE_PATH_OF_LV

#lvextend -L +100M /dev/oracle/lvm1

Before:

lvm1 oracle -wi-ao 100.00M

Executing:

[root@vm4 ~]# lvextend -L +100M /dev/oracle/lvm1

Extending logical volume lvm1 to 200.00 MB

Logical volume lvm1 successfully resized

After:

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After executing above commands you can verify the changed size by any of following

commands

#lvs, #lvdisplay, #lvscan

But if you check

#df -hT

it will be showing the old size only Because the filesystem is updated the changed in Logical Volume It can be updated by following command

#resize2fs /dev/oracle/lvm1

NOTE: In case of extending the LV is resized first and the filesystem after that But in case of shrinking a LV, filesystem is shrinked first followed by the shrink

in LV.

Before:

[root@vm4 ~]# df -hT

Filesystem Type Size Used Avail Use% Mounted on

/dev/mapper/oracle-lvm1

ext3 97M 5.6M 87M 7% /linux1

ext3 97M 5.6M 87M 7% /linux2

Executing:

[root@vm4 ~]# resize2fs /dev/oracle/lvm1

resize2fs 1.39 (29-May-2006)

Filesystem at /dev/oracle/lvm1 is mounted on /linux1; on-line resizing

required

Performing an on-line resize of /dev/oracle/lvm1 to 204800 (1k) blocks.

The filesystem on /dev/oracle/lvm1 is now 204800 blocks long.

After:

Filesystem Type Size Used Avail Use% Mounted on

ext3 194M 5.6M 179M 4% /linux1

ext3 97M 5.6M 87M 7% /linux2

Shrinking a Logical Volume (Offline):

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As we extended the size of Logical Volume, we can reduce the size also But in later case, it can

be done only offline That is the LV should be unmounted for reducing its size

For Shrinking a Volume:

1 Filesystem must be reduced first

2 Requires a filesystem check and cannot be performed online

3 #lvreduce can then reduce the volume

Now We have a Volume group "oracle" of size about 900Mb And two Logical vloumes lvm1 and lvm2 mounted on /linux1 and /linux2 respectively Size of lvm1 is 200Mb and size of lvm2 is 100Mb Now we'll reduce the size of lvm2 by 40Mb

Current status:

Step1: Unmont the volume:

#umount /linux2

Step2: Checking the filesystem:

#e2fsck -f LV_Path

#fsck -f /dev/oracle/lvm2

[root@vm4 ~]# e2fsck -f /dev/oracle/lvm2

e2fsck 1.39 (29-May-2006)

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

/dev/oracle/lvm2: 11/25688 files (9.1% non-contiguous), 8914/102400 blocks

This is to make sure that the filesystem is in a consistent state

Step3: Resizing the filesystem:

#resize2fs LV_Path Final_size

#resize2fs /dev/oracle/lvm2 60M

[Total size was 100Mb Reduction 40Mb So final size is 100-40=60]

[root@vm4 ~]# resize2fs /dev/oracle/lvm2 60M

resize2fs 1.39 (29-May-2006)

Resizing the filesystem on /dev/oracle/lvm2 to 61440 (1k) blocks.

The filesystem on /dev/oracle/lvm2 is now 61440 blocks long.

Step4: Now reduce the LV using #lvreduce

#lvreduce -L Size LV_Path

#lvreduce -L 40M /dev/oracle/lvm2

[root@vm4 ~]# lvreduce -L 40M /dev/oracle/lvm2

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WARNING: Reducing active logical volume to 40.00 MB

THIS MAY DESTROY YOUR DATA (filesystem etc.)

Do you really want to reduce lvm2? [y/n]: y

Reducing logical volume lvm2 to 40.00 MB

Logical volume lvm2 successfully resized

Before Reducing:

root@vm4 ~]# lvs

After Reducing:

After mounting:

ext3 194M 5.6M 179M 4% /linux1

ext3 59M 5.3M 50M 10% /linux2

Adding a Pysical Volume to a VG:

Now we have a Volume Group "oracle" of size 900Mb Suppose we used upto the maximum usable size So we need to extend the size of the VG

In this case we will create a new partition/a new hard disk, and will make it a Physical Volume and add it to the Volume group

Current status:

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oracle 3 2 0 wz n- 864.00M 624.00M

Now we created one more partition with id LVM

Step1:

First we have to convert it to physical volume

#pvcreate /dev/sda8

[root@vm4 ~]# pvcreate /dev/sda8

Current status of all Physical Volumes:

/dev/sda5 oracle lvm2 a- 288.00M 88.00M

/dev/sda8 lvm2 290.21M 290.21M

See /dev/sda8 is not the part of the VG oracle

Step2:

Now we will add the PV /dev/sda8 to Volume Group "oracle"

#vgextend -v oracle /dev/sda8

[ -v is for verbose To see what is happening]

[root@vm4 ~]# vgextend -v oracle /dev/sda8

Checking for volume group "oracle"

Archiving volume group "oracle" metadata (seqno 5).

Wiping cache of LVM-capable devices

Adding physical volume '/dev/sda8' to volume group 'oracle'

Volume group "oracle" will be extended by 1 new physical volumes Creating volume group backup "/etc/lvm/backup/oracle" (seqno 6).

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Volume group "oracle" successfully extended

After extending the VG with new Physical Volume:

VG #PV #LV #SN Attr Vsize VFree

oracle 4 2 0 wz n- 1.12G 912.00M

Now /dev/sda8 became a part of VG oracle

Removing a Pysical volume form a VG:

Before removing a physical volume from a volume group, you can make sure that the physical

volume is not used by any logical volumes by using the # pvdisplay command If the physical volume is still being used you will have to migrate the data to another physical volume using

the # pvmove command Then use the vgreducecommand to remove the physical volume Current status of Pysical Volumes:

In this example we will remove the Pysical Volume /dev/sda5 in which some Physical Extents are already used by some LV So They need to be migrated

The status of /dev/sds5 is

[root@vm4 ~]# pvdisplay /dev/sda5

Physical volume

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-PV Name /dev/sda5

VG Name oracle

PV Size 290.21 MB / not usable 2.21 MB

Allocatable yes

PE Size (KByte) 4096

Total PE 72

Free PE 22

Allocated PE 50

PV UUID 9l5HlF-h8Of-2J6D-TDr4-BY34-cREh-7U5zxm

Step1:

Migrate the used Pes using #pvmove command

[root@vm4 ~]# pvmove -v /dev/sda5

Finding volume group "oracle"

[output truncated]

Creating volume group backup "/etc/lvm/backup/oracle" (seqno 9) Step2:

Now reduce the Volume Group size by command #vgreduce

#vgreduce VG_name Removing_PV_Path

#vgreduce oracle /dev/sda5

[root@vm4 ~]# vgreduce oracle /dev/sda5

Removed "/dev/sda5" from volume group "oracle"

After Remvoing PV:

oracle 3 2 0 wz n- 864.00M 624.00M

/dev/sda5 lvm2 290.21M 290.21M /Now not part of oracleVG /dev/sda6 oracle lvm2 a- 288.00M 248.00M

Merging two Volume Groups:

Two different Volume Groups can be merged to a single Volume Group

Suppose we have two VGs "oracle" and "linux"

Current status of VGs are:

linux 1 0 0 wz n- 288.00M 288.00M

oracle 3 2 0 wz—n- 864.00M 624.00M

Now we are going to merge "oracle" and "linux" to get a single VG linux

We are using the command #vgmerge for this.

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#vgmerge merges two existing volume groups The inactive SourceVolumeGroupName will

be merged into the DestinationVolumeGroupName if physical extent sizes are equal and physical and logical volume summaries of both volume groups fit into

DestinationVolumeGroupName's limits

#vgmerge -v databases my_vg

merges the inactive volume group named "my_vg" into the active or inactive volume group named "databases" giving verbose runtime information

Step1:

we are going to merge "oracle" and "linux" to get a single VG linux

Make the source Volume Group inactive In this case source is oracle

#vgchange -a n oracle

umount the LV which uses the oracle VG then only u can inactivate it

[root@vm4 ~]# umount /linux1

[root@vm4 ~]# umount /linux2

[root@vm4 ~]# vgchange -a n oracle

0 logical volume(s) in volume group "oracle" now active

#vgmerge Destination Source

we are going to merge "oracle" and "linux" to get a single VG linux So

#vgmaerge -v linux oracle

[root@vm4 ~]# vgmerge -v linux oracle

Checking for volume group "linux"

Checking for volume group "oracle"

Archiving volume group "linux" metadata (seqno 1).

Writing out updated volume group

Creating volume group backup "/etc/lvm/backup/linux" (seqno 2).

Volume group "oracle" successfully merged into "linux"

linux 4 2 0 wz n- 1.12G 912.00M

[root@vm4 ~]# vgchange -a y linux

2 logical volume(s) in volume group "linux" now active

[root@vm4 ~]# mount /dev/linux/lvm1 /linux1

[root@vm4 ~]# mount /dev/linux/lvm2 /linux2

[root@vm4 ~]# mount

[output truncated]

/dev/mapper/linux-lvm1 on /linux1 type ext3 (rw)

/dev/mapper/linux-lvm2 on /linux2 type ext3 (rw)

/dev/sda5 lvm2 290.21M 290.21M

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/dev/sda7 linux lvm2 a- 288.00M 88.00M

Spliting a Volume Group into two:

We can split a Volume Group into two Volume Groups using the command #vgsplit

We have one VG oracle with 4 PVs We will split that VG oracle to oracle and another

VG redhat The PVs /dev/sda8 and /dev/sda9will be moved to redhat.

The syntax is as follows:

#vgsplit EXISTING_VG NEW_VG PATH OF PVs_TO _BE_MOVED

#vgsplit oracle redhat /dev/sda8 /dev/sda9

[root@vm4 ~]# vgsplit linux redhat /dev/sda8 /dev/sda9

New volume group "redhat" successfully split from "linux"

Before:

linux 4 2 0 wz n- 1.12G 912.00M

/dev/sda5 lvm2 290.21M 290.21M

After:

linux 2 2 0 wz n- 576.00M 336.00M

redhat 2 0 0 wz n- 576.00M 576.00M

/dev/sda5 lvm2 290.21M 290.21M

/dev/sda8 redhat lvm2 a- 288.00M 288.00M

/dev/sda9 redhat lvm2 a- 288.00M 288.00M

[root@vm4 ~]# vgchange -a y linux

2 logical volume(s) in volume group "linux" now active

[root@vm4 ~]# vgchange -a y redhat

0 logical volume(s) in volume group "redhat" now active

Tiêu đề	How to configure LVM
Trường học	University of Linux
Chuyên ngành	Computer Science
Thể loại	Hướng dẫn
Năm xuất bản	2025
Thành phố	New York

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Số trang	13
Dung lượng	163 KB